Particle abrasives such as diamond, various carbides and oxides are commonly used on grinding, cutting or lapidary tools and flexible abrasives such as sandpaper to provide means to cut, abrade or polish relatively hard materials such as metal, stone or composites. Generally, there has been no suitable process for applying such abrasive particles in other than random orientation and the various attachment means heretofore used are disadvantageous. They tend to operate by physically retaining the particles by imbedding them in a metal matrix, so that when the particles are approximately half worn, they are released from the metal matrix and are lost.
One method of retaining the particulate abrasive is to place the object to be coated in a bed of the particular abrasive, immersed in an electro-plating solution. Unfortunately, this requires a relatively large stock of abrasive particulate, which can be expensive if the particulate is diamond grit. Another method uses occlusion plating in which the particulate abrasive is circulated within a plating solution so that as particles come into contact with a substrate, they are tacked thereon. There are some variations to both of these processes, but in both cases, the article being coated is usually transferred to a second plating tank for finish plating after the initial tacking has occurred, thus requiring two tanks containing essentially identical plating solutions. When diamond grit is used, these processes are particularly disadvantageous, because generally, diamonds have a surface which is difficult to wet in an electro-plating process. Therefore, the plated metal matrix tends to physically retain the diamonds through envelopment rather than establishing a bond with individual diamonds. When tools constructed by these methods are used, there is a very small heat transfer path from the diamond to the substrate, so that the diamond tends to heat during use. The heating, if allowed to continue, causes cracking of the diamonds, or under extreme cases, sublimination and/or oxidation thereof, limiting the speeds and pressures at which such tool may be used.
What happens is that the plated metal, usually nickel, plates on the substrate metal, and builds up around the individual particles of abrasive. Therefore, the abrasive is held mechanically. The thickness of the plating equals roughly sixty percent of the diameter of the diamond. Therefore, it follows that the useful part of the diamond is about forty percent of its diameter, and when wear continues much beyond that point, the diamond is likely to come out. With both bed and occlusion systems, there is no particular orientation of individual grains of abrasive, and the abrasive, in most instances, presents a flat face rather than a sharp corner, as its cutting edge. Using these processes, an individual grain of abrasive is likely to attach to any bare metal surface forming the cathode of an electro-plating process with which it comes into contact. Therefore, control over the placement of abrasive particles is fairly limited.
Improved methods of attaching abrasive particles also includes first coating the abrasive particles electrolessly with a paramagnetic material, such as nickel, nickel phosphorous, cobalt or the like, paramagnetic material being that which is magnetizable but is not necessarily magnetized and is sometimes known as magnetic. The particles can then be attached to the substrate magnetically, either before or after the article to be coated is placed within an electro-plating tank.
All three methods produce a satisfactory result where the abrasive particles are to be distributed relatively evenly over the whole exposed surface. However, such even distribution with random grit orientations is not as desirable as would be possible if the process produced a pattern which controlled interruptions in the abrasive action to promote free cutting qualities of the tool either by allowing abraded material to escape therefrom or to assist any liquid coolant to wash away the debris produced by the action of the abrasing particles.
Existing techniques have produced patterns of abrasive, but they require the use of masks to produce even simple patterns. In addition, individual particles tend to attach to the substrate in a randomly oriented manner. Thus, an elongated particle may attach to the substrate with its axis either parallel or at right angles to the surface. This effect is undesirable. For example, in a saw blade advantage is gained by attaching elongated abrasive particles with the points projecting outwardly, and in lapping plates, a smoother cut is desired and may be obtained by laying the particles down flat.
Therefore, there has been a need for a process to selectively orient and place abrasive particles on a substrate in any pattern desired and/or with any orientation or combinations or orientations which also promotes cooling of the abrasive particles by providing an excellent heat transfer path away therefrom, and which allows the abrasive particles to be retained until they are almost completely worn away.